The bhastrika pranayama directly affects the nervous and circulatory systems. The intracranial pressure abruptly increases through each inhalation which, in turn, magnetises the cerebrospinal fluid.
The subtle body is inherently closed for a significant reason. Once it is made open, the subconscious awakens which in turn emerges our karmas. Hatha Yoga is the most powerful in awakening the kundalini. It is also the most dangerous.